1. Field of the Invention
The present invention relates generally to magnetic levitation systems for moving objects, and more specifically, to an improved magnetic levitation train system.
2. Description of Related Art
Halbach arrays, invented by Klaus Halbach in the 1980s for use in particle accelerators, represent a maximally efficient way to arrange permanent-magnet material when it is desired to produce a strong periodic magnetic field adjacent to the array. The beauty of the concept is that the effect of the cross-magnetized magnet bars in the array is to enhance the periodic magnetic field at the front face of the array, while canceling it back face of the array. Not only is the field enhanced, but analysis shows that in a long array the horizontal and vertical components are nearly purely sinusoidal in their spatial variation, with negligible higher spatial harmonics. If the Halbach array is then fabricated from high-field permanent-magnet material, such as NdFeB, peak fields near the front face of the array of order 1.0 Tesla are possible.
Particularly for lower-speed applications of magnetic levitation, such as for urban train systems, it is desirable to employ systems that are simple in construction and operation and that have low drag at urban speeds. Conventional maglev systems, that is, ones employing superconducting coils, or ones requiring servo-controlled electromagnets for levitation, appear to fall short on one or more of these counts.
Since it was first proposed the magnetic levitation of trains has been perceived to offer many potential advantages over conventional train technology. Besides the ability of maglev trains to operate a higher speeds than are deemed possible with wheel-and-rail trains, maglev trains should require less maintenance and be much smoother-riding and quieter than conventional rail systems. These perceived advantages have stimulated major development programs, particularly in Germany and Japan, to solve the technical and economic challenges of this new technology. These decades-long efforts have resulted in impressive demonstration systems, but as yet have not led to commercially operating rail systems in these countries. Factors that have slowed the deployment of high-speed maglev trains based on these technologies include technical complexity and high capital cost.
In an attempt to address these issues by taking advantage of new concepts and new materials, a different approach, called the Inductrack, was proposed. The first-proposed Inductrack disclosed in U.S. Pat. No. 5,722,326, titled xe2x80x9cMagnetic Levitation System For Moving Objectsxe2x80x9d, referred to herein as Inductrack I, employs special arrays of permanent magnets (xe2x80x9cHalbach arraysxe2x80x9d), on the moving train car to produce the levitating magnetic fields. These fields interact with a close-packed ladder-like array of shorted circuits in the xe2x80x9ctrackxe2x80x9d to levitate the train car. In this first form of the Inductrack, single arrays moving above the track produced the levitation. Whereas the Japanese maglev system employs superconducting coils and the German system requires servo-controlled electromagnets for levitation, the Inductrack is based on the use of high-field permanent magnet material, arranged in a special configuration called a Halbach array.
In the Inductrack maglev system Halbach arrays are used, located below the train car. When in motion the magnetic field of these arrays then induces currents in a special xe2x80x9ctrackxe2x80x9d made up of close-packed shorted circuits. Analysis has shown that the combination of the three elements, Halbach arrays, NdFeB magnet material, and close-packed circuits in the track result in the possibility of achieving levitation forces in excess of 40 metric tons per square meter of levitating magnets, corresponding to magnet weights of only a few percent of the levitated weight The use of Halbach arrays, high-field magnet material and close-packed circuits as employed in the Inductrack thus overcomes previous concerns, e.g., inadequate levitation forces, that led to questioning the practicality of using permanent magnets for maglev trains.
The theoretical analysis of the Inductrack leads to the evaluation of such quantities as the Lift-to-Drag ratio and the levitation power requirements as a function of train speed and of the magnet and track parameters. For the first-proposed, single-Halbach-array, form of the Inductrack, the L/D ratio is given by a simple relationship, given in Equation 1 below.                               ·                      Lift            Drag                          =                  kv          ⁡                      [                          L              R                        ]                                              (        1        )            
Here k=2Π/xcex, where xcex(m.) is the wavelength of the Halbach array. Note that the Lift/Drag ratio increases linearly with the train velocity and that its slope is determined by the inductance (self plus mutual) and the resistance of the track circuits. For a ladder-like track, that is one composed of transverse bars terminated at both ends with shorting buses, typical values for L and R give Lift/Drag ratios of the order of 300 at speeds of 500 km/hr typical of high-speed maglev trains. This ratio is high enough to make the levitation losses small (less than 10 percent) of the aerodynamic losses at such speeds. Also, for the Inductrack the xe2x80x9ctransition speed,xe2x80x9d the speed at which the lift has risen to half its final value (and also the speed where the lift and drag forces are equal) is low, of order a few meters/second (walking speeds). Thus the first-proposed form of the Inductrack would seem well suited for high-speed maglev train applications.
However, an examination of the first-proposed form of the Inductrack for its possible use in an urban setting, where the typical speeds are of order one-tenth of that of a high-speed maglev system, shows that the older system leaves something to be desired. Now, unless inductive loading of the track circuits is employed, the Lift/Drag ratio will have dropped to 30 or less. For an urban train car weighing, say, 20,000 kilograms, a Lift/Drag ratio of 30 at 50 km/hr corresponds to a drag force of about 6500 Newtons at a drag power in excess of 90 kilowatts.
It is an object of the present invention to provide a simple permanent-magnet-excited maglev geometry that provides levitation forces and is stable against vertical displacements from equilibrium but is unstable against horizontal displacements.
It is another object to provide an Inductrack system used in conjunction with the permanent-magnet-excited maglev geometry to effect stabilization against horizontal displacements and to provide centering forces to overcome centrifugal forces when the vehicle is traversing curved sections of a track or when any other transient horizontal force is present.
Another object of the present invention is to employ Inductrack track elements as the stator of a linear induction-motor drive and braking system.
Still another object of the present invention is to provide an alternate design of a linear pole system that has improved levitating force capabilities and lessened lateral stabilizer force requirements.
Another object of the invention is to provide a track for use with a linear pole array, where the track has improved properties for shielding the moving levitator poles from the effects of weather and from debris that might be deposited on the track.
Another object of the invention is to provide the levitating action by using a Halbach array attached to the moving object where the array is attracted upward to an iron-plate guideway and to further provide stabilizing means using additional Halbach arrays comprised of an upper Halbach array and a lower Halbach array, with an Inductrack track located between them.
These and other objects will be apparent to those skilled in the art based on the disclosure herein.
One embodiment of the present invention is a simple permanent-magnet-excited maglev geometry that provides levitation forces and is stable against vertical displacements from equilibrium but is unstable against horizontal displacements. An Inductrack system is then used in conjunction with this system to effect stabilization against horizontal displacements and to provide centering forces to overcome centrifugal forces when the vehicle is traversing curved sections of the track or when any other transient horizontal force is present. In some proposed embodiments, the Inductrack track elements are also employed as the stator of a linear induction-motor drive and braking system.
This new configuration eliminates the need for centering wheels, except possibly when the car is at rest in the station or upon failure of the drive while in transit In such cases, below a low critical speed, the wheels would restrain the system from lateral motion beyond a limit set by a predetermined spacing of the wheels from their guide rails.
One embodiment of the new configuration includes linear pole assemblies with iron poles, excited by permanent-magnet material. These elements are mounted on the moving car. They interact magnetically with the pole faces of a linear track, also fabricated from magnetic material, such as iron or steel. As shown, the poles exert a levitation force when they are displaced downward from the matching (attracting) poles on the track. The sideways attractive force exerted by each pole is balanced, when in the centered position, by the attractive force from the mating pole. This system is unstable against transverse displacements from the centered position. In this embodiment, lateral stabilization is provided by Inductrack Halbach arrays and the associated track circuits. As long as the car is moving so that the various elements are in the centered state, no currents will be induced in the Inductrack track, so that losses will be minimal. Only when there is a deviation from the centered position will currents be induced. Thus the energy losses from the system should be substantially less than those of a conventional Inductrack system, where currents must flow to provide the necessary levitation forces. In addition, the car will always be magnetically levitated, whether at rest or in motion, something that is not the case in the conventional Inductrack system.
Damping of vertical oscillations is provided by covering the face of the track magnet poles with a thin aluminum sheet. The planar Inductrack circuits may also function as the stator of a linear induction motor system using powered electromagnets on the moving car.
An alternate design of the linear pole system is provided that has improved levitating force capabilities and lessened lateral stabilizer force requirements. The track portion of this linear pole array has improved properties for shielding the moving levitator poles from the effects of weather and from debris that might be deposited on the track.
In an alternate embodiment of the invention, the levitating action is provided by a Halbach array attached to the moving object The array is attracted upward to an iron-plate guideway. Stabilizing means are provided by additional Halbach arrays comprised of an upper Halbach array and a lower Halbach array, with an Inductrack track located between them.